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API reference

Parameters, examples and live testing for every endpoint. Download the OpenAPI file to import into Postman / Apifox.

Pick an endpoint on the left; the right side shows parameter descriptions, code samples in several languages and example responses.
"Try it" sends real requests with the key you enter, and they are billed. The key is kept only in the current browser tab.

Getting started

Overview — Onefast API gives you GPT, Claude, Gemini, DeepSeek, Qwen and other leading models with one API key, compatible with the OpenAI, Anthropic and Gemini native protocols.
Quickstart — Create an API key and send your first request with cURL, Python or Node.js.
Authentication — How to send your API key, how to choose a group, and the quota, model and IP limits you can set on a key.
Groups & billing — What groups (routes) are, how prices are calculated, and when you aren't charged.

Chat completions (OpenAI-compatible) — Call any text model — GPT, Claude, Gemini, DeepSeek, Qwen and more — with the OpenAI Chat Completions format.
Responses API — OpenAI's next-generation Responses endpoint, used by default by Codex CLI and similar tools.
Claude Messages (Anthropic native) — Call Claude with Anthropic's official Messages API, with full native support for extended thinking, prompt caching, tool use and more.
Gemini native API — Call Gemini models with Google's official generateContent API, compatible with the Google GenAI SDK and Gemini CLI.
Tools & reasoning — Function calling, structured output, and controlling reasoning (thinking) for GPT, Claude and Gemini.
Prompt caching — Long prefixes you send repeatedly (system prompts, documents, tool definitions) can hit the cache, cutting input cost and latency significantly.

Image generation — Call GPT Image, Gemini (Nano Banana) and other image models with the OpenAI Images format, at 1K / 2K / 4K.
Video generation — Video runs as an async task — submit → poll status → download the result. Supports Seedance, Wan, Grok Imagine, HappyHorse, Gemini Omni and more.
Audio & embeddings — Text-to-speech (TTS), speech recognition (ASR) and text embeddings.

Claude Code — Use Onefast API in Claude Code, Anthropic's official command-line coding assistant.
Codex CLI — Use Onefast API in Codex CLI, OpenAI's official command-line coding assistant.
Gemini CLI — Use Onefast API in Gemini CLI, Google's official command-line assistant.
Cherry Studio — Add Onefast API to the Cherry Studio desktop AI client and use every model with one key.
Other clients & frameworks — Setup notes for common tools such as Cursor, Cline / Roo Code, LangChain, Dify and LobeChat.

API reference — Parameters, examples and live testing for every endpoint. Download the OpenAPI file to import into Postman / Apifox.
Model catalog — Every available model with live prices. When you're logged in, it shows all groups available to your account and their prices.
Errors — Error response formats, what common HTTP status codes mean and how to handle them.
FAQ — Frequently asked questions about integration, billing and choosing models.